I made this compilation of graphs the other day and sent it to nokia.
Nokia Lumia 800 Audio Quality issue
There is a thread on the nokia discussion forums where many people report audio problems, such as "no bass".
The 800 seems ok with an external amplifier, but with headphones it cut's off bass frequencies! IMD noise is subpar.
The performance of the 710 is catastrophic.
the shown Iphone 4S perfoms oustandingly well. Exact frequency response low IMD and low cross talk!
For reference I added the C7 I have, it performs pretty good! The Nokia N9 also performs well, I don't know what it is about the Lumias, but as of now I would say audiophiles stay away!
I hope this gets fixed in future Windows Phones from Nokia! then I would want one again